The present application relates to an optical element and a method for manufacturing the same. In particular, the present application relates to an optical element that selectively directionally reflects light in a specific wavelength band while transmitting light other than that in the specific wavelength band.
In recent years, building glass for high-rise buildings and houses and window glass for vehicles have been increasingly provided with layers for absorbing or reflecting some of sunlight. The glass described above is one of energy-conservation measures in order to prevent global warming and aims to reduce the load on air-conditioning systems that is applied thereto by an increase in indoor temperature when optical energy emitted from the sun enters an indoor space through a window. The optical energy emitted from sunlight primarily includes light in the visible region having a wavelength range of 380 to 780 nm and light in the near-infrared region having a wavelength range of 780 to 2,100 nm. In particular, since being irrelevant to human visibility, the transmittance of a window in the latter wavelength range, that is, in the near-infrared region, is an important factor that determines whether the window has highly transparency and highly heat-shielding properties.
As a method for shielding near-infrared light while maintaining the transparency in the visible region, for example, there may mentioned a method for providing window glass with a layer having a high reflectance in the near-infrared region. For example, Japanese Patent No. 4066101 has disclosed a laminated structural film including an oxide layer, a metal layer, and a dielectric material layer. Japanese Patent No. 4066101 has also disclosed that since the laminated structural film is used as a reflective layer, various properties, such as high visible light transmission properties, low radiation properties, high heat ray reflecting properties, and desirable reflective appearance, can be imparted to an optical element.
However, since this type of reflective layer is provided on flat window glass, specular reflection of incident sunlight can only be performed. Hence, light coming from the sky and specularly reflected reaches another outdoor building or the ground and is changed into heat by absorption, and as a result, an ambient temperature is increased. Accordingly, around the periphery of a building in which the reflective layers as described above are adhered to all windows, various problems occur, that is, for example, since a local increase in temperature occurs, a heat island phenomenon is promoted in an urban area, and lawns are not grown only in an area irradiated with reflected light.